Method of separating fatty acids



y 7- D. MYERS ET AL 2,421,157

METHOD, OF SEPARATING FATTY ACIDS Filed Jan. 20, 1942 INVENTOR.

Patented May 27, 1947 2,421,157 METHOD OF SEPARATING FATTY ACIDS Latimer n. Myers,

Muckerheide,

poration of Ohio Cincinnati, and Victor J. Silverton, Emerylndustries, 1110.,

Ohio, assignors ,to

Cincinnat Ohio, a cor- Application January 20, 1942, Serial No. 421,492 4 Claims. (01. 260-419) This invention relates to the art of separating higher fatty acids one from another and is directed particularly to the treatment of fatty acid stocks of the type from which stearic and oleic acids of commerce are obtained. The products are produced from materials such as tallow, brown grease, garbage grease and the like, and they are termed animal fatty acids.

The present invention is a continuation in part of copending Myers-Muckerheide application Serial No. 348,246, filed July 29, 1940, entitled Method of separating fatty acids, which has now issued into Patent No. 2,293,676, dated August 18, 1942. The present invention is directed particularly to an improved process for conditioning stocks of the type described in order to enable them to be separated more easily from one another in the separating process.

Oleic acid is a liquid, sometimes called red oil. Commercial stearic acid is a waxy solid. While the solid acid component of animal fatty acid is termed stearic, it is in fact comprised predominantly of stearic acid and palmitic acid, and these two components are present in typical animal fatty acids in a characteristic ratio, approximating what is commonly termed the eutectic mixture, 52.5% of palmitic and 47.5% of stearic acid, although the exact ratio varies somewhat with each specific stock. In the past, it has been impossible to separate the stearic and palmitic acids from one another, and the primary products of the fatty acid industry have, therefore, been glycerine, oleic, or red oil, and commercial stearic acid.

In the manufacture of commercial stearic acid in the past, the natural fats are chosen and blended to constitute a batch in which the solid fatty acids will have a ratio of 47.5% stearic acid to 52.5% palmitic acid; the reason for maintaining this eutectic ratio subsequen'ly is explained. After blending or selection, the fats are split into fatty acids and separated from the glycerine water. In many cases the fatty acids are then distilled to improve color and purity. Next, the mixed fatty acids are poured into pans to solidify, and are then chilled to approximately 40 F. The cakes so formed are wrapped in burlap, and pressed in large hydraulic presses. This operation removes a substantial percentage of the oleic acid, but by no means all of it, due to meacid components.

latitude is permissible, either in respect to the chanical entrainment and collapsed the cake.

These cakes are remelted, recast and pressed a second time at an elevated temperature, such as F., to remove additional oleic acid. This is called the hot pressing operation to distinguish it from the first pressing operation which is known as cold pressing.

At the temperature 'of the hot pressing operation, the solid fatty acids are soluble in the red oil, and pressing operation contains too high a percentage of solid fatty acids to be used for the purpose for which red oil is normally desired. This hot press red oil, therefore, must be reworked by further treatments or reincorporation with new batches of mixed fatty acids before it can become a useful commercial product.

If the indicated ratio of stearic to palmitic ,acid be not observed, the mixed fatty acids do not form the best crystal structure upon chilling, and it is difflcult to separate the red oil from the solid On this account, very little fats chosen to be processed, or in the composition of the ultimate products.

The commercial process just described is slow and expensive, and requires careful control and selection of the initial raw material to provide a balance which, ultimately, in the final product. Moreover, the number of raw fats and oils which may be combined or blended to provide the eutectic mixture is very limited. The process and the attendant commercial conditions, which have just been described, have existed for a period exceeding fifty years, and, outside of the development of the Twitchell fat splitting reagent, there has been little or no progress in the industry despite the urgent need for fatty acid fractions different from commercial stearic.

The present invention consists in producing substantially zero titre oleic acid, that is, one having a titre of between plus two and minus two, by removing the solid fatty acids from the oleic acid by solvent separation. We have also discovered that it is possible to fractionate the solid fatty acids in the course of separating them from the liquid fatty acids by dissolving the mixed fatty acids in a solvent, then crystallizing the solid acids and separating them from the liquid so the red oil fraction from the hot may not be desirable acids in two or more steps at progressively lower temperatures. By this method, it is possible to obtain solid fatty acid fractions, higher in stearic acid than palmitic acid, and other fatty acid fractions higher in palmitic acid than in stearic acid, and diiferent from eutectic mixes As many steps as desired may be employed and a corresponding number of fractions recovered.

Though it has been known for fifty years or more that a separation of solid--and liquid fatty acids could be made, at least approximately, by a method of this type, still the practical art has pursued universally the still older method of efiecting the separation by pressing operations. Our investigation indicates that one reason for the inapplicability of the proposed solvent separation process to commercial production has resided in the difficulty of obtaining precipitates susceptible to being filtered and washed in large scale production. We have determined that in order to obtain a substantially zero titre red oil, and useful solid acid components, it is desirable to use a polar type of solvent which is water miscible, such as methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, etc., that the water content of the solvent should not exceed 15% by weight, and that the concentration of the fatty acids in the solvent should not materially or substantially exceed 30% by weight. If the solvent be used with too much water present, then the separation of the solid fatty acids from the oleic acid is less than complete, so that the oleic acid is no better than that obtained by properly conducted pressing operations. If the concentration of fatty acids in solvent be too high, then the precipitate tends to form a slimy mass which cannot be handled or washed except perhaps in small quantities under laboratory conditions.

In order to apply the principle of solvent separation to commercial production of the animal fatty acids, it is requisite that the total amount of solvent employed in conducting the operation be not so great that its initial cost, its loss, its recovery costs and general handling will elevate the cost of the process above that of the presently utilized pressing methods. We have determined that it is feasible and practical, commercially, in large scale operations, to remove the solid from the liquid fatty acids by utilizing a concentration of acids in solvent of substantially 25 to 30% and by maintaining the strength of the solvent at 85 to 95%. These conditions provide a superior oleic acid, inhibit the entrainment of an undue quantity of oleic acid in the solid precipitate, and produce solid fatty acids suitable for various commercial uses.

The invention also comprises the fractionating of the solid fatty acids. Though this may be done where desired, apart from and independently of the solid and liquid fatty acid separation, still it is advantageous in many respects to perform the two operations conjointly. In order to do this, the solution is first chilled below the precipitating point of stearic acid, the first precipitate is filtered, and washed, and then the solution is further chilled and the precipitate again filtered. In this manner, any desired number of fractions may be obtained.

The degree of each drop of temperature is determined by the end products desired. Fractions tending to be higher in-stearic come out of solution first, and the fractions higher in palmitic at the lower temperatures.

In general, the fractions dominately high in palmitic are more difilcult to wash because of a tendency of them to entrain oleic acid. Such fractions are particularly suitable for soap making stocks because of the great tendency to lather in soaps made from palmitic acid. Where greater purity is desired, these fractions high in palmitic may be recrystallized from solution to reduce their content of oleic acid.

In the treatment of some stocks diiliculty sometimes is encountered in obtaining the formation of crystals having good filtering characteristics; sometimes the crystals are somewhat mushy and in this condition tend to clog a conventional filter cloth. The objective of the present invention has been to devise a process for conditioning the stock to be treated so that this difliculty does not occur.

We have discovered, briefly, that a stock having poor filtering characteristics can be converted and conditioned into a stock having good filtering characteristics by blowing air through the stock prior to the time it is subjected to the separation process. The exact mechanism accounting for the improved results obtained by this technique is not fully understood though it is believed that the air blowing process alters the neutral fat content of the stock.

If a definite predetermined but limited amount of neutral fat is present good filterable crystals are formed but if the neutral fat content exceeds a predetermined amount then either mushy crystals are obtained on the one hand, or crystals having good filtering characteristics may be obtained but such crystals may be of the same composition or substantially of the same composition as the mother liquor in which they grow.

The copending application Serial No. 427,491. filed January 20, 1942, entitled Method of separating fatty acids, which has now issued into Patent No. 2,298,501, dated October 13, 1942, discloses and claims a process in which fatty acid stocks are conditioned either by adding neutral fat to a fatty acid stock which is deficient in neutral fat or to a, process of adding fatty acids to a stock containing too much neutral fat.

In the process of the present invention the fatty acid stocks are conditioned by blowing air through them for a period of from five to twenty hours more or less. depending on the original condition of the stock. The time of air blowing is of more importance than the temperature maintained during the treatment. Air at high temperature tends to reduce the free fatty acid content of the stock very rapidly without materially conditioning the stock with respect to filtering. It is preferred in the process of the present invention to blow air through the stock at a relatively low temperature above the titre of the stock. Our experience has indicated that the optimum time for air blowing is approximately ten hours. Preferably the fatty acid stock is blown for a period of time sufiicient to increase the neutral fat content of the stock to a value within the range of from approximately .2% by weight of the stock to approximately il /2%.

The drawing illustrates by visual comparison the improvement in result obtained by treating fatty acid stocks in accordance with the process of the present invention.

Figure 1 of the drawing represents a fatty acid-solvent solution having poor filtering characteristics, for example, the solution may consist of a, thirty percent concentration of still stock dissolved in methanol and cooled to 24 C. After being permitted to settle for ten minutes it will be seen that no substantial physical separation of a fatty acid fraction from the solution is visible. The crystals are very fine and tend to remain in suspended condition in the solution at the given temperature.

Figure 2 represents a solution of the same concentration in the same solvent at the same temperature and likewise permitted to settle for ten minutes. The stock in this case has been blown with air for a period of ten hours prior to its introduction into the solvent. It will be seen that the solution shown in Figure 2 has settled rapidly and thereby separated from the solvent. Such a mixture has very good filtering characteristics.

The comparison test, represented in Figures 1 and 2, is useful as a guide in the practical application of the process. The stock is blown with air until results approximating those illustrated in Figure 2 are obtained'when a given concentration of the fatty acid stock is dissolved in a given solvent, such as 90% methanol, chilled to a given temperature and permitted to stand ten minutes. If suitable settling does not take place air blowing is continued. If settling takes place, as illustrated in the drawing or to a reasonable degree, then air blowing is discontinued and the stock is ready to be processed.

A control test of this sort may be conducted, for example, after five hours of blowing and then repeated hourly or every two hours, in order to ascertain the degree to which the stock has been conditioned,

The process of the pr esent invention is not necessarily applied to all fatty acid stocks; some need no conditioning whatsoever, some only a slight amount. Other, however, may be blown as long as ten or fifteen hours before the desired result is reached. Since fatty acid stocks are complex substances which vary from batch to batch the process of the present invention is a useful procedure in conditioning a material otherwise difflcult to separate. In the typical application of the process a sample may be taken from each batch of stock which is to be treated and subjected to a test of the type disclosed to determine whether or not it requires conditioning. The procedure is so simple that the test may be used as routine procedure. In the actual conditioning of the stock by blowing it with air, it is placed within a suitable tank or container, the temperature is preferably adjusted to a point just above the titre temperature and then air is blown through it in any suitable manner as, for example, by discharging air into the stockfrom a pipe located near the bottom of the container.

In a typical air blow operation the free fatty acid content is reduced somewhat, while the total fatty acid content of the stock remains substantially the same as before air blowing.

The principles of the general processes of separating fatty acids one from another in the commercial production of animal fatty acids are disclosed in detail in the aforesaid Myers-Muckerheide application Serial No. 348,246 and for illustration are repeated here.

Typical examples of the practice of the process are as follows:

Example 1 Distilled fatty acids consisting of a mixture of 75% tallow and 25% of garbage grease were dissolved in 90% methanol and processed at the rate of 1250# per hour in the solvent separation method, as previously described. Stock fresh from the stills yielded a very slimy cake which washed poorly yielding a stearic acid of l28.8 F.

titre. This stock was then blown with air for ten hours at a temperature of 130 F., the solids still precipitated in a s imy condition and a titre of 129.2. The stock was air blown an additional 8 hours and then filtered giving .a grainy dry cake, having desirable filtering characteristics. The solid acids had a titre of 130.1 F.

Example 2 A sample of stock which had been blown with air for 3 hours prior to distillation gave a poor filtering precipitate and a titre of 129.0 when run at a 15% concentration in methanol. After blowing with air for an additional 12 hours a granular, easily filterable precipitate was obtained and the stearic acid had a titre of 130.2.

This test shows that air blowing prior to distillation is also effectivebut cannot be relied upon completely.

. Example 3 Processing of another batch of stock consisting of distilled fatty acids from a mixture of 75% tallow, 25% garbage grease was processed as received from the stills. An extremely slimy filter cake was obtained which was almost impossible to filter on a rotary vacuum filter. In filtering a 20 inch filtering vacuum, 21 inchwash vacuum and a 23 inch vacuum for final solvent removal was necessary. The cake even with these vacuums contained only 25% solids and the solid acids produced had a titre of only 121.4.

The same stock was processed after air blowing for 18 hours at F. A granular slurry was obtained, the filter cake was dry and powdery, the filtration vacuum was 5 inches, wash vacuum '7 inches and vacuum on the solvent removal sections 9 inches. The cake contained 40% solids and the solid acids produced had a titre of 130.2 and an iodine value of 3.5.

Having described our invention, we claim:

1. A process for recovering purified fatty acid which comprises conditioning a fatty acid stock to enable crystal fractions having good filtering characteristics to be crystallized from a solvent solution of the stock cooled to a predetermined temperature, by passing air under pressure through the fatty acid stock fo a period of time sufilcient to effect an increase in the neutral fat content thereof preparing a solvent solution of the air-blown stock, cooling the solvent solution to eifeot crystallization of fatty acid therein, and filterin the crystallized fatty acid from the solution.

2. A process for recovering purified fatty acid which method comprises conditioning a fatty acid stock to enable crystal fractions having good filtering characteristics to be crystallized from a solvent solution of the stock cooled to a predetermined temperature, which process comprises blowing air through the stock for a period of approximately five to twenty hours in quantity sumcient to improve the formation of filterable crystals from a cooled solvent solution of the stock, then preparing a solvent solution of the stock, cooling the solvent solution to precipitate fatty acid crystals therein and removing the crystals by filtration.

4. A process for conditioning fatty acid stock to enable crystal fractions having good filtering characteristics to be precipitated from a solvent solution of the stock cooled to a predetermined temperature, which process comprises blowing 10 air through said stock for a period of time willcient to increase the neutral fat content of the stock to a value'within the range of from ap- LA'IHLE'R. D, MYERS. VICTOR J. MUCKERHEIDE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Myers Oct. 13, 1942 Number 

